Many types of articles, such as toolboxes for a portable power tool, are manufactured by using blow-molding techniques to produce a double wall body. By producing an article in this manner, one is able to easily create an article that has two, hard plastic walls with a buffering space between them, thereby resulting in a body with a multitude of desirable physical characteristics, such as strength, rigidity, scuff resistance, and impact absorption, but that is also relatively inexpensive to manufacture.
Typically, the blow-molding process involves the use of a mold consisting of two separate halves or portions having cavities of particularly desired shapes and sizes. Usually, one extrudes a large-diameter, sealed tube of molten material (commonly referred to as a “parison”), places the tube between the mold halves, and closes the mold around the tube. Fluid pressure is then introduced into the tube, forcing the molten tube against the walls of the cavities, conforming the tube to the shape thereof. The pressure is maintained until the molten material cools and solidifies. The pressure is then released, the mold halves are pulled apart, and the hardened article is ejected therefrom.
However, since fluid pressure is introduced to force the molten tube against the walls to create predetermined spacing between the walls, problems will be encountered for corner portions of the article where its surface geometry experiences sudden changes in orientation and/or plane of extension. In particular, to ensure that the thickness of each wall of the article at the corner portion is uniform and achieving a desired level, spacing of the two walls at the corner portion where sudden change of surface direction happens often have to be increased to avoid accidental adhesion of the two walls or non-uniformity in material strength. However, with the increased spacing between the walls, the corner portion is more vulnerable to external impact that easily results in deformation or dent of the corner portion.